Pneumonia is an inflammation of the alveolar space distal to the terminal bronchiole in the lung parenchyma. The inflammation seen in pneumonia is mostly caused by microorganisms such as viruses, bacteria, and fungi, but can also be caused by non-infectious causes (toxic substance inhalation, radiation damage, hypersensitivity reaction-pneumonitis, autoimmunity). Pneumonia can be observed in three forms: community-acquired pneumonia (CAP), hospital-acquired pneumonia (HAP), and ventilator-associated pneumonia (VAP). Patients with pneumonia usually present with cough, fever, sputum, chest pain, dyspnea, and hemoptysis. In addition, patients may have nonspecific symptoms. CAPs are caused by typical (S. pneumoniae) and atypical (C. pneumoniae, M. pneumoniae, and L. pneumoniae) agents. On presentation, fever, pulse rate, respiratory rate, oxygen saturation, blood pressure, and auscultation should be performed. Typical chest radiographic findings in the diagnosis of CAP include lobar consolidations, interstitial infiltrates, and/or cavitations. Acute-phase reactants may be elevated in response to infection and inflammation in pneumonia. The first decision to be made in cases of pneumonia is the determination of the need for hospitalization and the choice of antibiotherapy. If possible, cultures should be taken before antibiotics are started on the patient for whom hospitalization is planned. After 72 hours, in patients with no symptom improvement, the reason for treatment non-response should be evaluated, and antibiotherapy should be changed if necessary.